Membrane lipids are amphipathic molecules (amphiphilic molecules), i.e., they have a hydrophilic portion (polar head region) and a hydrophobic portion (long hydrocarbon chains). Three main groups of membrane lipids are known, i.e., phospholipids, glycolipids and cholesterin, as well as the subgroup ether lipids, which has branched chains.
Phospholipids are composed of four chemical components: fatty acids, a chemical platform that the fatty acids are bound to, a phosphate group, and an alcohol bound as an ester to the phosphate group. The chemical platform is either glycerin or sphingosine amino alcohol. The fatty acids vary in length, degree of saturation and degree of branching of their hydrocarbon chain.
U.S. Patent Application Publication 2002/0122873 A1 describes dip pen nanolithography (DPN) as a lithographic method for producing structures having dimensions of 10-1000 nm using a scanning probe microscope (atomic force microscope, AFM). In this connection, the tip of the scanning probe microscope is coated with the so-called ink, which is transferred by a driving force to the surface of a substrate. The macroscopic equivalent of DPN is writing with pen and ink, in this case, however, the pen having a nanoscale radius of curvature. The air humidity causes a liquid meniscus to form between the tip and the surface of a substrate which is then used to transfer the molecules from the tip to the surface. There, these molecules are chemically absorbed or patterned onto suitably prepared surfaces. Chemical, electrical, or magnetic forces are used as driving forces to apply molecules, clusters or nanocrystals to the substrate. Using this known method, it has so far only been possible to adjust the lateral dimensions of the structures applied to the surface.
In U.S. Pat. No. 6,756,078 B2, a method is described for applying phospholipids to a substrate, where the substrate, which is coated with a monolayer of a thioalkyl as a reactive substance, is first contacted by a linker compound, causing the linker compound to bind with the reactive substance to form a derivatized monolayer. It is only to this derivatized monolayer that the phospholipids are subsequently applied, and they chemically combine with the linker compound. The requisite covalent chemical bond between the phospholipids and the substrate is disadvantageous insofar as it limits the lateral mobility within the lipid bilayer.
U.S. Patent Application Publication 2002/0009807 A1 describes a method for applying phospholipids to regions of a substrate that have been provided with a film that promotes the deposition of lipid bilayers. In this connection, an aqueous phase, which contains the phospholipids, is applied to the substrate.
J. W. Carlson, T. Bayburt and S. G. Sligar, Nanopatterning Phospholipid Bilayers, Langmuir 2000, 16, 3927-3931, describes a method is known for patterning phospholipids on a substrate, regions of the layer of phospholipids on the surface of the substrate being removed by the tip of a scanning probe microscope. In the process, care must be taken to ensure that the layer of phospholipids does not dry out.
From S. Tristram-Nagle, H. I. Petrache and J. F. Nagle, Structure and Interactions of Fully Hydrated Dioleoylphosphatidylcholine Bilayers, Biophys. J. 75, 917-925 (1998), and S. Schuy and A. Janshoff, Thermal Expansion of Microstructured DMPC Bilayers Quantified by Temperature Controlled Atomic Force Microscopy, Chembiochem 7, 1207-1210 (2006), it is known that, at 20° C., 1,2-dioleoyl-sn-glycero-3-phosphocholin (DOPC) exists in a liquid-crystalline phase and that the thickness of a lipid bilayer is 3.4 to 3.5 nm, the precise value being dependent on the temperature, the air pressure and the air humidity.